Nozzle mix gunning operations employ an apparatus for pneumatically propelling dry or wetted granular material through a hose and nozzle combination at or onto a substrate located a distance from the nozzle. Common gunning materials include, for example, refractory and insulating products, which are applied so as to at least partially coat the surface of a substrate. Alternatively, sand or other abrasives may be gunned against the outer surface of a substrate to clean or otherwise condition the substrate.
Typically, the granular material to be gunned is ground to a desired particulate size and deposited within a sealed tank or hopper (known as a gun) where the particulates are mixed with a gas, such as air, at elevated pressure. The particulate/air mixture is thereafter released from the gun through a valve, whereupon the mixture passes through a hose and out the nozzle of the gunning apparatus, which is used to direct the mixture at the surface of the substrate.
Nozzle mix gunning operations are most effective when the granular material is gunned directly at the surface of the substrate, that is, at a 90.degree. angle or perpendicular to the surface. Gunning at an angle other than 90.degree. results in excessive rebound; that is, material that should stick to the substrate surface, which instead bounces off the surface. Excessive rebound results in the waste of a significant portion of the granulated material, which is not only costly, but also raises cleanup, contamination, and disposal problems.
With a straight nozzle, the mix can only be gunned at a 90.degree. angle to the surface when the surface is directly in front of the operator. If the surface to be gunned is inside an enclosed volume, such as a furnace, or if the operator must reach any appreciable distance across a substrate surface with a straight nozzle, it becomes impossible to gun the material at a 90.degree. angle to the surface, and increased rebound results.
Traditionally, a smoothly curved nozzle or haphazard arrangement of pipe fittings has been used to insure that the material is gunned at the proper angle. A curved nozzle allows an operator to apply a refractory coating to the entire inner surface of an enclosed space, without the need to enter the enclosure as would be required with a straight nozzle. However, pipe fittings and smoothly curved nozzles have two important shortcomings: (1) use of these nozzles results in an increase in divergence and material separation in the stream of gunned material, allowing a significant amount of material to impact the surface at an angle other than 90.degree., which increases rebound and pipe drip, and (2) a steel sweep will only last 5 to 30 minutes in pneumatic gunning, depending on the grade and thickness of the steel, because the impact of the abrasive gunned material wears away the interior surface of the nozzle.
Therefore, there is a need in the art for an improved device capable of overcoming the problems encountered with the prior art devices described above.